1. Field of the Invention
This invention provides a receptacle and arrangement for positively seating a thermocouple positioned to provide an indication of reactor coolant fluid temperature exiting the fuel assemblies of a nuclear reactor.
2. Description of the Prior Art
In order to monitor the performance of a core of a nuclear reactor, temperature indicating devices, such as thermocouples, are typically placed within the reactor. The thermocouples pass through conduits which guide the thermocouples through reactor internals components to a position above the core. A plurality of thermocouples so positioned above preselected core locations, or preselected fuel assemblies, provides a temperature profile of the core.
To provide an effective profile, not only must a plurality of thermocouples be utilized, but also the tips, or hot junctions, of the thermocouples must be positioned in the coolant stream as it exits preselected fuel assemblies and before the coolant stream is mixed with coolant from adjacent fuel assemblies. Further, because the thermocouples are exposed to a high temperature, pressure, and flow environment, failures occur necessitating replacement of specific thermocouples. The replacement is typically performed during refueling operations when the reactor upper internals are removed. In the event that the thermocouple tip is not reinserted to its original position, subsequent erroneous temperature indications can occur.
In prior art nuclear reactors, the protective conduits guiding the thermocouples have typically terminated within or about components of the upper internals, such as control element guide tubes or flow mixing devices. Such arrangements not only position the thermocouple junctions an extended distance above the upper core plate which is located above the fuel assemblies, but also do not allow visual inspection of the thermocouple tips to ascertain that they are properly extended into the flowing coolant stream. The latter deficiency is critical because it may result in the aforesaid erroneous temperature indications. Further, the orientation and configuration of the components required to support the thermocouples and their respective conduits impart a pressure drop to the flowing coolant, which it is desirable to minimize.
It is therefore desirable to provide a thermocouple receptacle and arrangement which overcomes the above mentioned deficiencies of the prior art. Such apparatus should provide a positive, repeatable seat for the thermocouples, a close proximity to the fuel assembly exits, a minimum pressure drop, and the ability to perform a visual inspection of thermocouple position to ensure a repeatable and correct indication of core thermal conditions.